Tuesday, February 22, 2011

University of Alberta researchers have linked the reproductive ecology of polar bears in Hudson Bay with declining litter sizes and loss of sea ice.

“Projected reductions in the number of newborn cubs are a significant threat to the western Hudson Bay polar-bear population,” said lead researcher Péter Molnár, from the Department of Biological Sciences. “If climate change continues unabated the viability of the species across much of the Arctic will be in question.”

Molnar and U of A colleagues Andrew Derocher and Mark Lewis used data collected beginning in the 1990s to analyze how long, during the polar bear’s hunting season, Hudson Bay is frozen over and the amount of energy pregnant females can store up before denning and birthing.

“An early spring-ice break up reduces the hunting season, making it difficult for pregnant females to even support themselves, let alone give birth to and raise cubs,” said Derocher.

Pregnant polar bears take to a maternity den for up to eight months and during this time no food is available and they survive on their fat stores.

In the early 1990s, researchers estimate, 28 per cent of energy-deprived pregnant polar bears in the Hudson Bay region failed to produce a litter. Researchers say energy-deprived pregnant females will either not enter a maternity den or they will naturally abort.

Using mathematical modeling to estimate the energetic impacts of a shortened hunting season, the research team calculated the following scenarios:

· If spring break up in Hudson Bay comes one month earlier than in the 1990s, 40 to 73 per cent of pregnant female polar bears will not reproduce.

· If the ice breaks up two months earlier than in the 1990s, 55 to a full 100 per cent of all pregnant female polar bears in western Hudson Bay will not have a cub.

The polar-bear population of western Hudson Bay is currently estimated to be around 900, which is down from 1,200 bears in the past decade. The number of polar bears across the Arctic is estimated to be between 20,000 and 25,000.

“Because the Hudson Bay polar bears are the most southerly population, they are the first to be affected by the global-warming trend,” said Molnar. “However, if temperatures across the Arctic continue to rise, much of the global population of polar bears will be at risk.”